I just bought a cheap bi-metal coil oven thermometer from Update International ($3.99). I'm curious if there is a way to calibrate the thermometer. Otherwise, I'd have no way of knowing if it's my oven that's inaccurate or the thermometer.

I could immerse the thermometer in boiling water, but that's not a very assuring method for me. Calibrating at 212 F only gives me the response of the thermometer at that temperature and not at higher temperature ranges used in baking. Is there a way I can calibrate at higher temperatures to get a few more points for a calibration curve?

Dunking a four dollar bimetal thermometer in boiling water might cause corrosion on the bimetal strip, so I wouldn't do that.

Second, anything you might use to calibrate a four dollar thermometer at oven cooking temperatures of say, 250 to 450 will cost more than it is worth to calibrate it. You can either trust the thermometer (which is probably close enough) or get a professional probe or infrared thermometer which will cost significantly more.

You might get a second thermometer like you have and see if they agree.

Do you have a reliable candy thermometer? This would help, but I gave up on bimetal thermometers long ago. These days for such things I rely on decent digital probe thermometers, like the Polder or the CDN.

One thing to remember, however, is that ovens cycle quite a bit above and below the target temperature over the course of cooking. So when calibrating an oven, you must factor this in, and set for average temperature.

Exact oven temperature is really only a major concern if you do a lot of baking, though. For the roasting of meats, and so on, if you cook to temperature, and not time, most ovens are close enough right from the factory.

Oh, and then there are things like frozen pizzas, and TV dinners. Don't get me wrong, I like those as much as the next guy. My oven is calibrated so those are done perfectly right in the middle of the estimated times on the boxes

if the food thermometer cannot be calibrated, it should still be checked for accuracy using either method. Any inaccuracies can be taken into consideration when using the food thermometer, or the food thermometer can be replaced. For example, water boils at 212 °F. If the food thermometer reads 214 °F in boiling water, it is reading 2 degrees too high. Therefore 2 degrees must be subtracted from the temperature displayed when taking a reading in food to find out the true temperature. In another example, for safety, ground beef patties must reach 160 °F. If the thermometer is reading 2 degrees too high, 2 degrees would be added to the desired temperature, meaning hamburger patties must be cooked to 162 °F.

Exact oven temperature is really only a major concern if you do a lot of baking .For example, water boils at 212 °F. If the food thermometer reads 214 °F in boiling water, it is reading 2 degrees too high.